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Before the National Rifle Association dropped hundreds of thousands of dollars to try to flip a competitive, Democratic-held Senate seat, the gun-rights group’s chief lobbyist apparently gave the race’s Republican challenger a heads-up.

Chris Cox, the top political strategist for the NRA’s Institute for Legislative Action (NRA-ILA), assured Montana Republican Matt Rosendale that the group would spend heavily to support his bid to unseat Sen. Jon Tester, Rosendale told attendees at a July event in Washington.

PAY DIRT exclusively obtained audio of Rosendale’s remarks, which good-government groups say raise serious questions of potentially illicit coordination between Rosendale and an independent political group supporting his campaign.

“I fully expect the NRA is going to come in… in August sometime,” Rosendale said in response to a question about independent political spenders in the race. “The Supreme Court confirmations are big. That’s what sent the NRA over the line. Because in ’12, with [Republican Senate nominee Denny Rehberg] they stayed out, they stayed out of Montana. But Chris Cox told me, he’s like, ‘We’re going to be in this race.’”

Rosendale was slightly off in terms of timing, but the NRA did come through as Cox apparently promised. Early this month, the group spent more than $400,000 on ads hitting Tester over the precise issue that Rosendale mentioned—the senator’s votes on Supreme Court nominations.

Rosendale’s remarks are potentially problematic, as the NRA-ILA, a 501(c)(4) “dark-money” group, is legally barred from coordinating its ad buys with a federal campaign. As explained by nonprofit tax law attorney Holly Schadler, illegal coordination may occur “if the organization has substantial discussions with the campaign about an expenditure, or if the organization informs the campaign about a planned communication related to the campaign and the campaign signals its agreement with the suggestion to make that communication.”

Brendan Fischer, the director of Federal Election Commission reform programs for the Campaign Legal Center, said Rosendale’s remarks, together with the eventual ad campaign he alluded to, might satisfy the “three-pronged” legal test for impermissible coordination. The three prongs are payment, content, and conduct.

“The payment prong is satisfied because the ads were paid for by somebody other than Rosendale; the content prong is satisfied because the ads expressly advocate against the election of Rosendale’s opponent; and the conduct prong can be satisfied by Rosendale assenting to the request or suggestion of the entity paying for the ad: the NRA,” Fischer said.

An investigation into potential wrongdoing would likely hinge on the question of whether Rosendale encouraged or otherwise signed off on Cox’s pledge to get involved in the race. Rosendale did not recount his reply to Cox in response to the questioner, meaning he could claim that no such assent was offered.

Neither the Rosendale campaign nor the NRA-ILA responded to requests for comment.

Fischer’s group has also filed an FEC complaint alleging the NRA is illegally coordinating with a number of federal campaigns through the use of a common vendor. NRA-ILA’s independent expenditures have been routed through a company called Starboard Strategic. That company appears to be a clone of another vendor, OnMessage, which works with the same campaigns that the NRA is—ostensibly, independently—supporting with huge ad buys. The Trace first reported on the vendor overlap that led to CLC's complaint.

The complaint alleged that OnMessage, which shares staff and office space with Starboard Strategic, was using insight gleaned from media-buying work for the candidates’ campaigns to inform the NRA’s separate advertising strategies in each race.

Like other senators in competitive races this year, Rosendale’s campaign has paid OnMessage for media services, with payments totaling about $445,000. The NRA’s expenditures for its anti-Tester ads, notably, were paid to Starboard Strategic.